William Rousan, 57, was scheduled to be executed at 12:01 a.m. Wednesday for killing a southeast Missouri farm couple 21 years ago. Rousan's attorneys are seeking clemency from Gov. Jay Nixon. A three-judge panel of the 8th U.S. Circuit Court of Appeals denied a request for a stay and the full court on Tuesday refused to reconsider the case. Rousan's attorneys appealed to the U.S. Supreme Court.

Several states, including Missouri, now use compounded execution drugs purchased from unnamed pharmacies. Courts so far have allowed executions to move forward, though some dissenting judges have questioned the practice.

Missouri has executed one death row inmate each month since November. Another execution, of Russell Bucklew, is scheduled for May 21. Only Texas, with seven executions, and Florida, with four, have executed more inmates than Missouri's three so far in 2014.

Rousan was sentenced to death for killing 62-year-old Grace Lewis, of rural St. Francois County, in 1993. He was sentenced to life in prison for killing her 67-year-old husband, Charles. The killings were part of a plot to steal cattle from the Lewis farm near Bonne Terre - just a couple of miles from the prison where Rousan faces execution.

Rousan also lived in the same area of St. Francois County, about 70 miles southwest of St. Louis. On Sept. 21, 1993, Rousan, his 16-year-old son, Brent, and his brother, Robert, concocted a plan to kill the couple and steal their cattle. Authorities said at trial that William Rousan was the ringleader.

The men drove by the farm, and William Rousan pointed out the cattle to steal. They parked about two miles away and hiked through the woods to the farm. They watched as the couple returned home. Charles Lewis began cutting the lawn with a riding mower while his wife spoke to the couple's daughter on the phone.

Brent Rousan ambushed Charles Lewis, shooting him six times. Grace Lewis told her daughter on the phone she heard gunfire and stepped outside to check on the commotion. Brent Rousan shot her several times. She managed to go back into the home, but William Rousan followed her, placed a garment bag over her head and carried her outside.

He turned to his son and said, "Finish her off." Brent Rousan fired a single shot into the side of her head.

The men placed the bodies in a tarp and put them near a shed. Later that night, they returned, along with another Rousan brother, loaded the bodies in the Lewis' pickup truck, and took two cows, a VCR, jewelry, a saddle and other items.

For almost exactly a year, they got away with the crime. The couple seemingly had vanished without a trace.

In September 1994 investigators received a tip -- a VCR sold to a pawn shop by a sister of William and Robert Rousan was the one stolen from the Lewises. It was the break police had been waiting for.

The bodies were found buried in a shallow grave covered with concrete and a pile of horse manure on the farm where William Rousan was living at the time. After a four-day manhunt, Rousan was arrested while hiding in a barn on Sept. 20, 1994. He was caught with a .22-caliber semi-automatic rifle and a knife.

Brent Rousan pleaded guilty to two counts of first-degree murder and was sentenced to life in prison without the possibility of parole. Robert Rousan cooperated with prosecutors and pleaded guilty to second-degree murder. He was released from prison in 2001, Missouri Department of Corrections spokesman David Owen said.

The Obama administration will unveil a major climate change plan Monday aimed at a large reduction in greenhouse gas emissions from the nation's coal-burning power plants, a senior administration official told CNN.